Take control of home heating

Thermostats used to be primitive on-off switches that required a lot of tweaking -- up a hair to ward off a chill, then down a hair to cool off.

Modern versions have keypads and digital readouts that control heating, cooling, humidity and even the amount of fresh air taken in through a heat-exchanger. And they're programmable.

That's the best feature, and makes them probably the most effective energy-saving investment you can make.

When you're asleep and toasting under a quilt, the thermostat turns itself down until morning. When you're at work, the thermostat setback saves more fuel, then automatically rises to a comfortable setting before you get home.

Two misconceptions

Old or new, dial or keypad, thermostats are often misused in two ways that waste energy. Both stem from common misconceptions about how furnaces work.

*The first is that you get more heat faster by temporarily boosting a thermostat above the normal setting. That doesn't work because furnaces produce heat at a constant rate. If you want more, the furnace has to run longer. There is no overdrive setting for extra heat production.

*The second is that it doesn't pay to reduce the temperature when you're not there (or asleep) because the furnace will use up the saved fuel climbing back to the old setting.

Some people think thermostat setbacks waste even more energy as the furnace somehow works harder and longer to recover temperature than it does to maintain temperature. It doesn't. As the Department of Energy (DOE) puts it, "This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature."

Aha, say the skeptics. The up and down is a wash so why bother? Because the furnace uses less fuel at the lower setting -- and the savings add up when you extend the down time, for instance, overnight, during the day while you're at work, or both. It will take a little time to rewarm the house. But a short warm-up is peanuts compared to daylong and nightlong savings.

Expected savings

Houses and household living patterns differ, so there is no single savings equation. But the DOE says that a 10- to 15-degree setback for only eight hours will save from 5 to 15 percent of total heating costs. The National Association of Homebuilders says programmable thermostats typically offer savings of 10 to 15 percent without compromising comfort.

That last point is key. Yes, your house will be colder at times, but you won't be there (or awake) to notice. And if you don't want to cower under the covers until the house to warms up, simply program the furnace-on setting 15 minutes or so before the alarm goes off. Programmable thermostats are not an extra-sweater solution to saving energy.

To estimate your savings, use this rule of thumb: save about 1 percent of heating costs per degree of setback over eight hours. That's about 3 percent per degree over 24 hours.

Though two setback periods are possible (eight hours overnight and eight hours during work hours), in most households even one major setback can save enough to pay for the thermostat in a year or two. It's probably the best energy-saving investment you can make -- and gets even better when you include similar savings in the summer with central air conditioning.

Buying the right model

A new version of the traditional, round manual-adjust thermostat costs about $35. An entry-level programmable is about $10 more. Prices rise with programming capacity to $100 and up for a top-line thermostat with touch-screen technology that can handle several setbacks a day seven days a week -- every day different if you want. Those units can control heating, cooling, humidity and ventilation -- aside from telling you when it's time to replace the air filters.

The bells and whistles are nice, but many top-line thermostats offer more technology than you'll ever use.

So before buying, it's smart to make a weeklong schedule of possible setback times lasting at least four hours. Then match the schedule to the thermostat programming capacity. If you want only one setback overnight, the most basic and inexpensive unit will do.

Some units also offer remote control, which seems like overkill on a thermostat that's already programmed to your lifestyle. But one worthwhile extra is built-in battery backup. It eliminates the need to reprogram the unit, which can take a while, after a power failure.